Known electronic systems for controlling the output torque or output power of an internal combustion engine are typically concerned with controlling regions of maximum (peak) engine output torque to thereby achieve any of a number of engine/drivetrain performance and/or engine/drivetrain operational efficiency goals. No systems are presently known, however, for controlling engine output torque or output power characteristics in engine output torque or engine output power regions remote from regions of peak engine output torque.
An example of a situation wherein it would be desirable to control engine output torque characteristics only in an engine output torque region remote from peak engine output torque occurs in vehicles having torque converters operating in a so-called "torque converter" mode at least part of the time. Torque converters are known and commonly used in the automotive and heavy duty truck industries to control the transfer of engine output torque to at least partially automated vehicle transmissions, and one example of a known system 10 employing such a torque converter is illustrated in FIG. 1. Referring to FIG. 1, an internal combustion engine 12 is coupled to a torque converter 14 of known construction which is itself coupled to a transmission 16 having a tailshaft or propeller shaft 18 extending therefrom. As shown in partial cutaway and partial cross-section, torque converter 14 includes an impeller or pump 20 affixed to a torque converter adaptation assembly 22 that is driven by an output shaft of the engine 12, and a turbine 24 affixed to a turbine shaft 26 of transmission 16. A lockup clutch 28 is disposed between impeller 20 and turbine 24, and is coupled to a charge pump 30 of transmission 16 via fluid passageway 32.
Transmission 16 is a known semi-automatic, automated or fully automatic transmission having a number of automatically selectable gear ratios. Propeller shaft 18 extends from transmission 16 and is operable to drive one or more vehicle wheels (not shown) as is known in the art.
System 10 includes a control computer 34 which interfaces with a number of engine operational sensors and subsystems (not shown) as is known in the art, and is connected to an engine fueling system 36 via a number N of signal paths, wherein N may be any integer. In operation, control computer 34 is operable to determine appropriate fueling signals, based on current engine operating conditions as is known in the art, and provide corresponding fueling signals to fueling system 36. Fueling system 36 is, in turn, responsive to the fueling signals provided thereto by control computer 34 to supply fuel to engine 12. Engine 12 is designed and calibrated such that it is responsive to the fuel supplied thereto via fueling system 36 to produce a characteristic engine output torque curve over a range of engine speeds as is known in the art.
Referring to FIG. 2, one example of a known characteristic engine output torque curve 38 over a range of engine speed values is shown. Engine output torque curve 38 includes a region 40 of rising engine output torque followed by a region 42 of peak engine output torque followed by a region 44 of decreasing engine output torque, wherein regions 40, 42 and 44 sequentially correspond to increasing engine speeds. The region 42 of peak torque defined between engine speeds ES0 and ES1 is typically referred to as the "torque dwell" region, after which engine output torque decreases with increasing engine speed to a so-called "governed" engine speed ES2. The term "governed engine speed" is defined for the purposes of this document as that engine speed at which the engine 12 achieves a "rated" or advertised output power.
In the operation of system 10, the torque converter 14 is operable in a so-called "torque converter" mode during vehicle launch and low speed operations, whereby the lockup clutch 28 is disengaged and the impeller 20 therefore rotates at the speed of the engine 12 while the turbine 24 is actuated by the impeller 20 through the fluid shown disposed therebetween in FIG. 1. In this operational mode, torque multiplication occurs through the fluid coupling such that the transmission turbine shaft 26 is exposed to more input torque than is being supplied by the engine output shaft 22, as is known in the art. When the engine 12 is otherwise engaged with certain gear ratios of transmission 16, the torque converter is generally operable in a so-called "lockup" mode, whereby the lockup clutch 28 is engaged and the impeller 20 is therefore secured to the turbine 24 to thereby directly couple the torque converter adaptation assembly 22 to the turbine shaft 26, as is known in the art. The transmission 16 is operable, in a known manner, to mechanically or hydraulically control the operational status of the lockup clutch 28. As shown in FIG. 1, for example, a fluid passageway 32 couples the lockup clutch 28 to the charge pump 30 of transmission 16, whereby the charge pump 30 controls the hydraulic pressure of fluid supplied thereto to operably engage and disengage lockup clutch 28.
Transmitting torque through torque converter 14 during "torque converter" mode is known to be an inefficient transfer of engine operating power. However, the "torque converter" mode of operation is desirable, for at least short durations for example, to provide for clutch-less vehicle launches and to multiply engine output torque during vehicle launch conditions. Accordingly, manufacturers of semi-automatic, automated and/or fully automatic transmissions specify a so-called "stall turbine torque limit" that corresponds to a maximum allowable transmission input torque during a "torque converter stall" condition which is a known industry term and is defined for the purposes of this document as an operating condition wherein the vehicle wheels are locked, the transmission is in gear and the engine is operating at full/maximum or peak power. The peak engine output power (and corresponding stall turbine torque) typically occurs in region 44 of the engine output torque curve 38 of FIG. 2 (i.e. between engine speed ES1 corresponding to the high engine speed boundary of the torque dwell region and engine speed ES2 corresponding to governed engine speed).
In order to meet the so-called stall turbine torque limits specified by transmission manufacturers, designers of internal combustion engines heretofore typically selected a torque converter exhibiting optimum operational characteristics and then designed the engine output torque characteristics to yield maximum engine performance without exceeding specified input limits of the transmission during torque converter operation including, for example, a stall turbine torque limit. Unfortunately, such design strategies sometimes resulted in sacrificing vehicle performance during torque converter lockup operation. What is therefore needed is a system for controlling engine output torque in torque regions remote from the torque dwell region during torque converter mode of operation. Such a system would enable an engine designer to configure the engine output torque curve 38 so as to limit engine output torque in engine output torque region 44 during torque converter mode of operation, while providing for greater available engine output power in lockup mode of torque converter operation.